Read resistor bands and capacitor codes, then estimate a via

Parts on the bench carry their values as colour bands or three-character codes. Ohmforge reads both and writes the result straight into the selected part, as a normal undoable edit.

Resistor colour bands

Open the RC low-pass filter + Bode plot template and select R1. In the Properties panel choose Resistor color bands… (the same helper is under Instruments). Because R1 is 1 kΩ, the helper opens with its marking already set: brown, black, red, gold.

Choose Number of bands — four bands for two significant digits, five or six for three — and pick the colours from left to right, starting at the end with the first stripe. The tolerance band follows the multiplier; a sixth band gives the temperature coefficient in ppm/K. The result shows:

• the nominal value, for example 1 kΩ,
• Tolerance and Range (brown, black, red, gold: ±5 %, 950 Ω to 1.05 kΩ),
• Preferred series — the IEC 60063 series that contain the value. 1 kΩ is in every series from E6 to E192; 4.7 kΩ is in E6, E12, E24 and E192; 4.99 kΩ only in E96 and E192. A value outside every series is a hint that you misread a colour.

Set five bands to yellow, violet, black, brown, brown (4.7 kΩ ±1 %) and choose Apply resistance to R1. R1 now reads 4.7k; Ctrl+Z restores 1k. Tolerance and temperature coefficient are shown for reference only; they do not change the schematic.

The Resistor Color Code tool works the other way round too: enter a resistance and a band count and it returns the colours. It never rounds silently — 1234 Ω has four significant digits, so it asks for another value instead of guessing.

Capacitor codes

Select C1 and choose Capacitor code…. The dialog starts from C1's value: 100 nF is marked 104 (10 × 10⁴ pF). Type another code, for example 472, to read 4.7 nF, or 2R2, where R is the decimal point (2.2 pF).

Under Find the code for a value enter a capacitance with an SI prefix, for example 4.7u: the code is 475. Use this code copies it to the code field. Choose Apply capacitance to C1 to write the value into the schematic; Ctrl+Z undoes it. Codes cover 0.01 pF to 99 µF with two significant digits; a value such as 1.234 nF has no exact code and the dialog says so. The marking says nothing about voltage, dielectric or tolerance — check the datasheet.

Estimate a via

Open the PCB Via Estimator from the Ohmforge home page. Enter the finished hole diameter after plating, the plating thickness, the barrel length (usually the board thickness) and the current. A 0.4 mm hole with 35 µm plating through a 1.6 mm board has a copper ring of 0.0478 mm² and about 0.575 mΩ at 20 °C, so 1 A drops 0.575 mV.

The via result is an ideal DC copper barrel. It is not a current-capacity, temperature-rise, high-frequency or fabrication check, and it leaves out pads, plating variation and heating. Confirm finished dimensions with your board fabricator.